Disruption of functional connectivity may be a key feature of bipolar disorder (BD) which reflects disturbances of synchronization and oscillations within brain networks. We investigated whether the resting electroencephalogram (EEG) in patients with BD showed altered synchronization or network properties. Resting-state EEG was recorded in 57 BD type-I patients and 87 healthy control subjects. Functional connectivity between pairs of EEG channels was measured using synchronization likelihood (SL) for 5 frequency bands (δ, θ, α, β, and γ). Graph-theoretic analysis was applied to SL over the electrode array to assess network properties. BD patients showed a decrease of mean synchronization in the alpha band, and the decreases were greatest in fronto-central and centro-parietal connections. In addition, the clustering coefficient and global efficiency were decreased in BD patients, whereas the characteristic path length increased. We also found that the normalized characteristic path length and small-worldness were significantly correlated with depression scores in BD patients. These results suggest that BD patients show impaired neural synchronization at rest and a disruption of resting-state functional connectivity.
Keywords: BD, bipolar disorder; Bipolar disorder; C, clustering coefficients; DSM-IV, diagnostic and statistical manual of mental disorders, the 4th-edition; DTI, diffusion tensor imaging (image); EEG, electroencephalogram; EOG, electrooculogram; Eg, global efficiency; El, local efficiency; Electroencephalogram; FA, fractional anisotropy; FDR, false discovery rate; Functional connectivity; GABA, gamma-amino butyric acid; Graph theory; L, characteristic path length; MADRS, Montgomery–Asberg Depression Rating Scale; MEG, magnetoencephalogram; MRI, magnetic resonance imaging; NBS, network-based statistics; NC, normal healthy control; PLI, phase lag index; Resting state; SCID, Structured Clinical Interview for DSM Disorders; SL, synchronization likelihood; Synchronization likelihood; WASI, Wechsler Abbreviated Scale of Intelligence; WM, white matter; YMRS, Young Mania Rating Scale; b, node betweenness centrality; fMRI, functional magnetic resonance imaging; s, node strength; γ, normalized clustering coefficients; λ, normalized characteristic path length; σ, small-worldness.